Richard Bateman, RWC’s Product Marketing Manager, talks about the best products and materials to use when plumbing in boilers and cylinders, as well as the importance of safety valves.

Just like the kitchen is seen as the heart of the home, the same can be said of boilers and cylinders for plumbing and heating systems. Without them, a home would struggle to function, so they must work well and be plumbed in with due care and consideration to ensure they are safe for users.

As one of the more complex areas of plumbing, there’s much to bear in mind when installing boilers and cylinders, including the legal requirements, the best materials to use, setting up for the installation, and how to ensure the safety of the system.

The legal stuff
Let’s start with the legalities. Given the safety requirements and demands of installing boilers and cylinders, a variety of skills and legal certifications are needed. 
First and foremost, any installation, maintenance, and commissioning must be completed by a Gas Safe-registered engineer. 

For unvented cylinder installations, installers must complete a G3 training course covering the G3 regulations. Upon completion, installers can obtain a certificate to confirm their competency. This qualification lasts for five years and further training is required to obtain a new certificate after its expiry date.

You can also refer to the Gas Safe Register website for news on legislation, testing, and maintenance to stay abreast of updates and best practice. 

Plastic or copper?
One common misconception of boiler and cylinder plumbing is that you cannot connect them using plastic pipes and plastic push-fit fittings. While it is true that with some systems and some plastics there could be a risk of the plastic becoming distorted by the heat, advances in boiler technology mean that some systems are now compatible with the latest generation of plastics.

For example, while RWC’s JG Speedfit pipe and fittings must not be used on gas, our Speedfit PEX and PB pipe, plus selected fittings, are rated to be used in heating systems with working temperatures up to 82°C, and up to 114°C during instances of system malfunction.

Many new boilers operate within this range, so you do not need to be concerned about using plastic pipes and fittings on boilers, yet it is advisable to always check with the boiler manufacturer to ensure you select the materials that will work best for the specific case. Ultimately, this makes installations much simpler and quicker by allowing you to use push-fit connections, rather than needing to solder joints or use compression fittings. 

Safety first
Once the choice of pipework has been determined, then the next step is to prepare for the set up and installation, and this is where the safety hat comes on. Remember that before installing a vented or unvented system, the Local Authorities Building Control (LABC) must be notified.

The first stage of setting up for a boiler and cylinder installation is following Part G of the Building Regulations, section G3, and having the necessary safety devices ready. This includes a temperature relief valve (TPR) and a pressure relief valve (PRV). Installing multiple safety valves provides reassurance that if one fails another will deliver the extra safety needed.

These safety devices are required in the event of the cylinder overheating or over-pressurising. A common cause of overheating is a build up of sediment from hard water, acting as an insulator within the cylinder. This will often cause an over-run and make the cylinder heat for longer, and then lead to potentially catastrophic damage.

Finally, when working on a boiler or hot water cylinder, the Benchmark form must be completed and left with the customer. This will enable the end-user to prove the safety of the boiler or cylinder.

Safety valve functions
Moving onto installation, there are a number of safety valves that should be installed to safeguard systems against pressure, backflow, and temperature.

Starting with pressure, there’s a cold feed to the cylinder and this can be susceptible to big surges in pressure which, in turn, could cause damage to the cylinder. To avoid this, best practice would be to fit a PRV, providing a constant amount of pressure, capped between 2.1-3.5 bar. The cylinder manufacturer usually stipulates this setting.

Installers should also fit a safety relief valve alongside the PRV, set at a higher pressure of anything up to 8 bar. If the PRV fails and the cylinder starts to over-pressurise, the safety relief valve will open and discharge cold water out of the system. In older systems, this might be in the way of water discharging out the side of the building.

To avoid backflow, although not commonly included, a double check valve should be integrated onto the cylinder. As the water in the cylinder is classified as a fluid category three risk, a double check valve should be fitted on the cold water supply that feeds into it, in case the hot water expands and goes down the hot water supply and contaminates the water.

With regards to managing temperature, it is best practice to have a temperature and pressure relief valve in case the safety relief valve doesn’t kick in, or stops working for any given reason. As the name suggests, this valve not only senses a rise in pressure, it also reacts to temperature. If 95°C is exceeded in the cylinder, and the pressure side of the valve fails, the temperature side would lift and discharge water off the system. 

Ambient temperature can also have an effect on pressure within the cold water pipework feeding a cylinder. Therefore, an expansion vessel should be fitted to ensure that this does not cause over-pressurisation during normal operation.

Zone valves
An absolutely final failsafe for cylinder installations is the zone valve. This is a motorised electrical valve that closes in the event of the pressure and temperature relief valve failing.

These valves work by wiring a dual thermostat installed within the cylinder to the two-port zone valve, which controls the hot water going out to the home’s outlets. It is recommended that the dual thermostat is set to 70°C. If the cylinder goes above the set temperature, the zone valve will kick in and shut the supply off to the tap.

Once all valves are fitted and the cylinder has been installed, the system can start to be filled using a filling loop. By law, this filling loop, which is either a flexi hose or hard pipe, must be disconnected until the next service. This is also the case for filling loops connected to boilers.

As all installers should know, boilers and cylinders should never be underestimated. These vital parts of the plumbing and heating system can create serious damage and pose huge hazards if not plumbed in correctly